The present invention is directed to a leg prosthesis for adapting to a thigh stump, as known from German published patent application DE-A-199 53 972. It comprises an adapter for a knee joint, which adapter is anchored in the femur stump of the patient with a post. At the distal end the adapter emerges from the thigh stump and there it can be coupled to an artificial knee joint, as known, for example, from European Patent EP-B-0 358 056.
A prosthetic lower leg, which in turn carries an attached prosthetic foot at its distal end, is coupled to the knee joint. This prosthetic foot can pivot from a pointed (toes-down) foot position to a cocked (toes-raised) foot position.
The knee joint according to the proposal of European Patent EP-B-0 358 056 is formed such that for the transition from the extended position to the bent position, it carries out a combined rolling and sliding motion about a pivot axis. In contrast to a pure hinge joint, the knee joint of this generic type of leg prosthesis is formed such that the distance of a point of the knee joint lying in front of the pivot axis, when viewed dorsally, to the end of the prosthetic lower leg continuously decreases. In other words, the distance of a point lying in front of the pivot axis, when viewed ventrally instead, to the end of the prosthetic lower leg constantly increases.
One problem for patients with a partially amputated upper leg is that, among other things, he must walk with the healthy foot in a strong toes-down foot position, in order to allow the prosthetic foot to swing through forwardly with the leg prosthesis for a new step. This is true independent of whether the prosthetic foot can pivot on the prosthetic lower leg or is rigidly attached. The necessity of bringing the healthy, natural foot into an exaggerated or extreme toes-down foot position, so that the prosthesis can swing through, causes a rather non-physiological type of motion and thus a great stress is placed on the spine while walking.
From the generic type shown in this patent, it can be gathered that between at least one support point lying in front of the pivot axis, when viewed dorsally, and/or a support point lying in front of the pivot axis, when viewed ventrally, and the prosthetic foot, a force-transmitting element is arranged which, upon bending of the knee joint, moves the prosthetic foot from a toes-down foot position or neutral foot position of the artificial foot in large measure to the toes-raised foot position. In this way, the necessity to bring the healthy, natural foot into a non-physiological toes-down foot position, so that the artificial leg can swing through, should no longer exist, and the sequence of movement should appear more natural.
Although the leg prosthesis of the generic type has already achieved clear progress relative to the basic state of the art, it does not allow the generation of a dynamic bionic gait, i.e., a gait sympathetic with nature. The reason for this is to be seen in that the swinging movement of the prosthetic lower leg is the same over wide ranges. In contrast, in a natural leg, the movement of the knee joint changes as a function of its bending position. Thus, in the bent state, i.e., in the range of about 90°, the knee can move relatively freely. With decreasing bending angle, i.e., for extension of the leg, the resistance against further bending increases. In the extended state of the leg, the knee joint is de facto rigid.
The lack of changing resistance forces against further bending of the knee thus impairs the dynamic bionic gait for the leg prosthetic of the generic type shown in this patent.